The covalently-closed, circular forms of bacterial plasmids have been found to be nonintegratively associated with their host's folded chromosomes. The influence of these complexes in plasmid maintenance will be investigated. Also, different chromosomal mutations that increase the level of plasmids per chromosome have been identified. The influences of these mutations on plasmid incompatibility will be examined. BIBLIOGRAPHIC REFERENCES: Cress, D. E. and B. C. Kline. 1976. Isolation and characterization of Escherichia coli chromosomal mutants afffecting plasmid copy number. J. Bacterial. (in press).